Hello Borda, Yours is only a Doubt and Not a Repair, I also take time to explain. The Quick Charge Chargers Work in conjunction with the cell phone, so that there is "Quick Charge", the Charger and cell phone must be compatible with this System. When you connect the Cellphone, a "Compatibility Detection" communication occurs and if they are compatible, the "Quick Charge" is activated. This load consists of increasing the load power and is achieved by increasing the Voltage. During a fast charge the voltage goes up to 9Volts, the current stays constant. In this way, by delivering more power, you get the fast charge. This also leads to a secondary problem, which is the warming of the Unit. Your Second Question is like "A Myth" that circulates. Here something very common happens, if I or someone else answers something, maybe a friend of yours comes out who tells you otherwise and that's how these Myths are born. I tell you that for you to get this doubt out and be convinced of the Truth you have to resort to service manuals of each cell phone model and Examine the charging circuit for "Yourself"! If you examine any charging circuit of a Motorola or Samsung cell phone or any other, you should see that the battery has a Voltage Protection system, which is located between the charger and the Battery, bone when the Battery Reaches the "Charge Limit" A Transistor "DISABLETS" the voltage that is sent to the battery. And it remains in Standby until it lowers the Voltage and activates again. This indicates that there is no problem with leaving the cell phone charging overnight (its protection system turns the power OFF when the battery is fully charged). One thing to keep in mind if you are a Repairman, there are IMITATION Cell phones and you can easily identify them by their Hardware. In these Imitation phones it is not certain that they have any protection circuit for Disconnection. So While You Use Cell Phones from Recognized and Original Brands, Motorola, Samsung or LG. You should not worry about leaving them connected all night. This Caution is only for Chinese Imitations. If you have doubts about this, it is best that you find out for yourself through the interpretation of the Service manuals, if you are patient, check the Load circuits. Only by interpreting them for yourself and for sure you can agree, or not, with my opinion.